Conventionally, to adjust the phase of a digital signal, it is required to perform signal interpolation (oversampling) to take out a signal of a required phase. For example, Non Patent Literature 1 mentioned below discloses a technique in which a signal of a desired phase is generated by using a digital filter and a filter coefficient corresponding to each phase interval to be adjusted, thereby interpolating the digital signal.
Furthermore, Patent Literature 1 mentioned below discloses, as a specific configuration thereof, a technique related to a variable digital filter that can change frequency characteristics without disturbing characteristics of the digital filter. Coefficient that can interpolate different phases by changing a multiplier factor of a multiplier are stored in a memory address, coefficient data that interpolates a phase closest to a desired phase value is read out, and the multiplier factor of the multiplier is changed, thereby obtaining an interpolated value close to a true value. Consequently, the memory capacity is reduced, while enabling the frequency characteristics to be finely adjusted without disturbing the filter characteristics.